1. Field of the Invention
This invention relates to shiftable, blocked change speed gear devices, preferably multiple countershaft floating mainshaft transmissions, having resiliently yieldable shifting means utilizing blocker and jaw clutch assemblies for substantially simplifying shifting of the transmissions, and in particular relates to shiftable, blocked, change gear transmissions normally driven by one-way prime movers and utilizing improved blocker and jaw clutch assemblies effective to allow engagement of at least one selected ratio gear under static conditions.
2. Background of the Invention
In the design of transmissions, particularly heavy duty transmissions, such as for example are used in trucks, there has existed for a long time the problem of shifting the transmission to the various gear ratios, which problem is even greater when the transmission is provided with an auxiliary transmission section of the range or the splitter type for increasing the number of gear ratios. In most known transmissions, the shifting process is either relatively difficult and/or the shifting mechanism is relatively complex. Thus, there has been a continuing effort in the design of transmissions to improve the shifting, to improve the rapidity of shifting, to reduce the complexity of the shifting mechanism, and to reduce its costs. Hence, without detracting in any way from the operability or desirability of many of the shifting mechanisms previously known, it may be stated that in the present invention these general objectives are accomplished to even a greater degree than has been previously possible.
Particularly, most previously known transmissions have required a relatively high level of operator skill or necessarily utilized synchronizers, of which many different types are known, for causing the speed of the jaw or tooth clutch members to be substantially synchronized prior to permitting their interengagement during a shifting sequence from one speed ratio to another speed ratio. While the use of synchronizers does permit the shifting operation to be performed, their use, as is already known, imposes certain requirements of weight, space and power which is desirable to ease, or avoid entirely, if possible.
These and other problems incident to previously known transmissions were set forth and acknowledged in U.S. Pat. Nos. 3,799,002, entitled "TRANSMISSION WITH RESILIENTLY LOADED MAIN SHAFT GEARS"; 3,910,131, entitled "TRANSMISSION WITH SNAP SHIFT"; 3,921,469, entitled "TRANSMISSION WITH RESILIENTLY LOADED MAIN SHAFT GEARS"; 3,924,484, entitled "SENSOR UNBLOCKING RAMPS"; and 3,983,979, entitled "SENSOR UNBLOCKING RAMPS"; all hereby incorporated by reference and assigned to the same assignee as the present application. Apparatus is disclosed in the above mentioned patents which effectively meets the problems while providing a reliable, effective and efficient transmission, particularly for heavy duty use.
While both forms of the inventions disclosed in said patents, namely, those using blockers and those not using blockers, are effective for carrying out the objectives thereof, it has been noted that for the usual reasons both noise and clutch tooth wear can be minimized by the use of blockers as set forth in said patents and since the date thereof a considerable amount of investigation has been carried out related thereto, both for simplifying of the blocker structure and for improving the operation of said blockers and of transmissions utilizing same. Blockers of various types are well known in the prior art and examples thereof may be seen by reference to the above mentioned patents and to U.S. Pat. No. 3,503,280, entitled "BLOCKER DEVICE", issued to W. C. Bopp, and assigned to the assignee of this application.
Blockers of the type illustrated in the above mentioned patents are generally nondeformable devices designed to prevent, or block, the engagement of the axially engageable jaw clutch members of a jaw clutch when said members are rotating at substantially different speeds, i.e., are not substantially synchronized. Transmissions utilizing such blockers are referred to herein as "blocked transmissions". Blocked transmissions are transmissions utilizing blockers to prevent jaw clutch engagement if the members of the jaw clutch are not substantially synchronized. This is in contrast to "synchronized transmissions" which utilize synchronizer clutches to cause the jaw clutch members to be synchronized. The relatively nondeformable blockers utilized with many of the prior art blocked transmissions are generally rotationally retained on one clutch member for rotation therewith with a limited amount of relative rotation (3.degree.-15.degree.) provided. The one clutch member is usually that clutch member rotationally fixed to the transmission mainshaft. The blocker and the one clutch member will define an array of first projections or teeth or the like which will allow the one clutch member to move relatively axially towards the other clutch member when in alignment but will block such relative axial movement when said blocker is rotated in either the clockwise or counterclockwise direction relative to the one clutch member. The blocker is designed to be in positive frictional contact with the second clutch member during an engaging operation and will thus tend to rotate with the second clutch member. Random frictional contact will usually cause, or tend to cause, the blockers to rotate with the second clutch members at times when a clutch engagement is not attempted.
By way of example, assuming the use of a relatively nondeformable blocker as disclosed in the above mentioned prior art and that the clutch members are rotating in a clockwise direction, if the first clutch member is rotating faster than the second clutch member, upon initiation of an engaging operation the blocker will be rotated counterclockwise relative to the first clutch member and the blocker will prevent axial movement of the first clutch member towards the second clutch member. If the second clutch member is rotating faster than the first clutch member, the blocker will be rotated clockwise relative to the first clutch member and the blocker will prevent axial movement of the first clutch member towards the second clutch member. If the first clutch member initially rotates faster, then slower than the second clutch member, the blocker would, relative to the first clutch member, rotate in a clockwise direction from an initial counterclockwise rotated position relative to the first clutch member towards a relatively clockwise rotated position. During the relative rotation, for at least a limited period of time, the blocker would align with the first clutch member and cease to block axial movement thereof towards the second clutch member. Such relative movement of the clutch members and the blocker is generally referred to as "passing through synchronous". The clutch will "pass through synchronous" or "cross synchronous" as the two clutch members reach a substantially synchronous rotation, and the clutch engaging operation, or the gear shift, should be completed at this time. As the blocker is designed to be in positive frictional contact with the second clutch member only during a clutch engaging operation to prevent undue frictional wear, it is possible, under certain conditions, that the blocker can be set up on the "wrong side of synchronous" at the initiation of a clutch engaging operation, i.e., referring to the above example, rotated clockwise relative to the first clutch member when the first clutch member was rotating faster than the second clutch member or vice versa. Under such conditions, especially if the driven device is stopped, it is difficult or impossible to cause the blocker to "pass through synchronous" and the transmission cannot, without undue manipulation, be shifted into the desired gear ratio.
In a blocked transmission driven by a one-way prime mover, the blocked clutch members have an inherent problem of achieving jaw clutch engagement under certain static conditions, i.e., when the driven device is standing still and the transmission is in neutral. When a blocked transmission of the twin countershaft type, as is illustrated in U.S. Pat. Nos. 3,799,002 or 3,924,484, is in neutral with the master clutch engaged, the gearing will, for at least a period of time, rotate while the output or main shaft is stationary. The aforementioned condition tends to place the blockers in the "upshift position", i.e., that position associated with a dynamic upshift wherein the jaw clutch member rotating with the main shaft must be rotated faster than the clutch member rotating with the gearing to cause the clutch to pass through synchronous. When the gearing comes to a stop, the blockers remain in the "upshift position" and, because it is difficult and/or impossible to rotate the main shaft with the transmission in neutral, a reversing of the gearing or an auxiliary aligning of the blockers and jaw clutch members is required to achieve a jaw clutch engagement.
In compound, blocked transmissions of the type seen in U.S. Pat. Nos. 3,799,002 and 3,924,484, relative overspeeding of the auxiliary transmission gearing by the main shaft can be achieved by the operator momentarily shifting the transmission from neutral into reverse as reverse gear is normally not a blocked gear. But this is obviously an inconvenience, a highly undesirable technique, and might hamper the commercial acceptability of an otherwise highly successful transmission.
Mechanisms for selectively and/or automatically reverse rotating the mainshaft are believed to be an effective auxiliary method of obtaining clutch engagement of a blocked transmission at a static condition. However, due to manufacturing, space, cost and operational considerations, such mechanisms may not be satisfactory in certain situations.